Structural determinants of transmission at large hippocampal mossy fiber synapses.

TY - JOUR

T1 - Structural determinants of transmission at large hippocampal mossy fiber synapses.

AU - Rollenhagen, Astrid

AU - Sätzler, Kurt

AU - Rodríguez, E Patricia

AU - Jonas, Peter

AU - Frotscher, Michael

AU - Lübke, Joachim H R

PY - 2007

Y1 - 2007

N2 - Synapses are the key elements for signal processing and plasticity in the brain. To determine the structural factors underlying the unique functional properties of the hippocampal mossy fiber synapse, the complete quantitative geometry was investigated, using electron microscopy of serial ultrathin sections followed by computer-assisted three-dimensional reconstruction. In particular, parameters relevant for transmitter release and synaptic plasticity were examined. Two membrane specializations were found: active zones (AZs), transmitter release sites, and puncta adherentia, putative adhesion complexes. Individual boutons had, on average, 25 AZs (range, 7-45) that varied in shape and size (mean, 0.1 microm2; range, 0.07-0.17 microm2). The mean distance between individual AZs was 0.45 microm. Mossy fiber boutons and their target structures were mostly ensheathed by astrocytes, but fine glial processes never reached the active zones. Two structural factors are likely to promote synaptic cross talk: the short distance between AZs and the absence of fine glial processes at AZs. Thus, synaptic cross talk may contribute to the efficacy of hippocampal mossy fiber synapses. On average, a bouton contained 20,400 synaptic vesicles; approximately 900 vesicles were located within 60 nm from the active zone, approximately 4400 between 60 and 200 nm, and the remaining beyond 200 nm, suggesting large readily releasable, recycling, and reserve pools. The organization of the different pools may be a key structural correlate of presynaptic plasticity at this synapse. Thus, the mossy fiber bouton differs fundamentally in structure and function from the calyx of Held and other central synapses.

AB - Synapses are the key elements for signal processing and plasticity in the brain. To determine the structural factors underlying the unique functional properties of the hippocampal mossy fiber synapse, the complete quantitative geometry was investigated, using electron microscopy of serial ultrathin sections followed by computer-assisted three-dimensional reconstruction. In particular, parameters relevant for transmitter release and synaptic plasticity were examined. Two membrane specializations were found: active zones (AZs), transmitter release sites, and puncta adherentia, putative adhesion complexes. Individual boutons had, on average, 25 AZs (range, 7-45) that varied in shape and size (mean, 0.1 microm2; range, 0.07-0.17 microm2). The mean distance between individual AZs was 0.45 microm. Mossy fiber boutons and their target structures were mostly ensheathed by astrocytes, but fine glial processes never reached the active zones. Two structural factors are likely to promote synaptic cross talk: the short distance between AZs and the absence of fine glial processes at AZs. Thus, synaptic cross talk may contribute to the efficacy of hippocampal mossy fiber synapses. On average, a bouton contained 20,400 synaptic vesicles; approximately 900 vesicles were located within 60 nm from the active zone, approximately 4400 between 60 and 200 nm, and the remaining beyond 200 nm, suggesting large readily releasable, recycling, and reserve pools. The organization of the different pools may be a key structural correlate of presynaptic plasticity at this synapse. Thus, the mossy fiber bouton differs fundamentally in structure and function from the calyx of Held and other central synapses.

KW - Animals

KW - Rats

KW - Models, Animal

KW - Synaptic Transmission physiology

KW - Imaging, Three-Dimensional

KW - Synapses physiology

KW - Rats, Wistar

KW - Neuronal Plasticity physiology

KW - Microscopy, Electron

KW - Mossy Fibers, Hippocampal physiology

KW - Neurotransmitter Agents physiology

KW - Synaptic Vesicles physiology

KW - Animals

KW - Rats

KW - Models, Animal

KW - Synaptic Transmission physiology

KW - Imaging, Three-Dimensional

KW - Synapses physiology

KW - Rats, Wistar

KW - Neuronal Plasticity physiology

KW - Microscopy, Electron

KW - Mossy Fibers, Hippocampal physiology

KW - Neurotransmitter Agents physiology

KW - Synaptic Vesicles physiology

M3 - SCORING: Zeitschriftenaufsatz

VL - 27

SP - 10434

EP - 10444

JO - J NEUROSCI

JF - J NEUROSCI

SN - 0270-6474

IS - 39

M1 - 39

ER -